Electrophotography is a useful process for printing images on a receiver (or “imaging substrate”), such as a piece or sheet of paper or another planar medium, glass, fabric, metal, or other objects as will be described below. In this process, an electrostatic latent image is formed on a photoreceptor by uniformly charging the photoreceptor and then discharging selected areas of the uniform charge to yield an electrostatic charge pattern corresponding to the desired image (a “latent image”).
After the latent image is formed, charged toner particles are brought into the vicinity of the photoreceptor and are attracted to the latent image to develop the latent image into a visible image. Note that the visible image may not be visible to the naked eye depending on the composition of the toner particles (e.g. clear toner).
After the latent image is developed into a visible image on the photoreceptor, a suitable receiver is brought into juxtaposition with the visible image. A suitable electric field is applied to transfer the toner particles of the visible image to the receiver to form the desired print image on the receiver. The imaging process is typically repeated many times with reusable photoreceptors.
The receiver is then removed from its operative association with the photoreceptor and subjected to heat or pressure to permanently fix (“fuse”) the print image to the receiver. Plural print images, e.g. of separations of different colors, are overlaid on one receiver before fusing to form a multi-color print image on the receiver.
Electrophotographic (EP) printers typically transport the receiver past the photoreceptor to form the print image. The direction of travel of the receiver is referred to as the slow-scan, process, or in-track direction. This is typically the vertical (Y) direction of a portrait-oriented receiver. The direction perpendicular to the slow-scan direction is referred to as the fast-scan, cross-process, or cross-track direction, and is typically the horizontal (X) direction of a portrait-oriented receiver. “Scan” does not imply that any components are moving or scanning across the receiver; the terminology is conventional in the art.
However, toner is sometimes transferred to locations on the receiver where it is not desired. This results in print images with more noise or lower contrast than desired. This phenomenon is referred to as “background development.” It is desirable to reduce background development to provide high image quality.
It is known to remove developer from a development member used to develop the latent image into the visible image. U.S. Pat. No. 3,927,640 to Smith describes a magnetic gate for stopping developer flow when it is desired to purge the development system. U.S. Pat. No. 3,981,272 to Smith et al. describes a development system with a movable sump for storing developer. Neither of these schemes has any effect on background development.
U.S. Pat. No. 7,442,484 to Uchinokura et al. points out that removing toner particles from the surface of the photoreceptor can be difficult, and those particles can result in undesired background development. The scheme described in this patent uses chemically-prepared toner and an induction fuser, and is therefore not useful for many electrophotographic printers using alternatives to those components.
U.S. Pat. No. 6,108,499 to Cernusak describes cleaning waste toner off a photoconductor drum using a cleaning blade. However, Cernusak points out background development can result from electrical and mechanical wear on the photoconductor. Cleaning the waste toner produces mechanical wear.
U.S. Pat. No. 5,550,619 to Komakine et al. describes a removal roller for removing excess toner from a latent image holding member to reduce background development.
There is an ongoing need, therefore, for an improved way of reducing background development that is applicable to a wide range of electrophotographic printers.